Johnson 6 + 8hp: Carb differences

Hello,<br /><br />it seems the difference in power only comes from different carbs<br /><br />Can anybody of you explain it ?<br /><br />The carbs seem basicly quite equal except for a special device outside the housing near the throttle pivot.<br />It's a lever arrangement with little rods of different length.<br />Is it a kind of throttlening device ?<br /><br />Greetings from Germany<br /><br />Nordy

Re: Johnson 6 + 8hp: Carb differences

Guten Tag, Nordy.<br /><br />They get different horsepowers from the same block by varying carb throat size, exhaust tuning, timing advance curves, more. Just replacing the 6Hp carb with an 8Hp one is probably only get you part of what you want. You probably won't end-up with an 8Hp and you could damage what you have. I discourage doing it.

Re: Johnson 6 + 8hp: Carb differences

The 8hp has a completely different intake than the 6hp and there is no simple conversion without replacing the block/crankcase assembly. The 8hp has four reeds per cylinder and the 6hp has three reeds per cylinder. The crankcase face, intake manifold and reed plate are all different, as well as the carbs. Also, the 6hp has a stop molded into the throttle cam to stop it before achieving the same advance as the 8hp. <br />Note: These are only some of the differences I've noticed and they may vary by year. For instance, the earlier 7.5hp version of this motor had the three reeds per cylinder set-up. The four reeds per cylinder set-up seems to coincide with the conversion to prop-rated over powerhead rated horsepower, making the 8hp more than 0.5hp stronger than the 7.5 it replaced...<br />- Scott

Re: Johnson 6 + 8hp: Carb differences

Guten Tag Willy, hello Scott,<br /><br />thank you.<br /><br />Regards Nordy